We will evaluate and further perfect a newly developed non-invasive method to assess pulmonary artery pressure using a microbubble expansion technique (MET). This method relies on external recording of sound emitted as injected microbubbles oscillate, within the pulmonary artery, proportional to the compressive pressure within the pulmonary artery. This method is called bubble ultrasonic ringing pressure (BURP). This project consists of a search for optimal methods of injection of the MET material, recording of the BURP signals, and analysis of the data. The BURP method will be tested for accuracy in static pressure systems and pulsatile pressure systems in vitro; and investigation of accuracy and reproducibility of measurement of pulmonary artery pressure in dogs will be performed. Dogs with normal pulmonary artery pressure and dogs with pulmonary hypertension will be used as models of the human situation. The use of this BURP method in altered circulatory states also will be examined.